The air conditioning of a cabin in a vehicle, in particular in a motor vehicle, often makes use of a heater which is directly or indirectly connected to the cooling fluid circuit of the vehicle engine. Under normal operating conditions, i.e. over a certain range of rates of flow of the fluid (generally a liquid) flowing through the heater, the flow of liquid takes place through the heater with substantially no head loss. However, when the engine is operating at high speeds, a pressure difference appears between the inlet and the outlet to the heater. In order to counteract this additional pressure, the liquid circuit is provided with a rated bypass valve that responds to a predetermined value of pressure difference to oppose said pressure difference and return the device to normal operating conditions.
In fluid circuits of this type that are already known, as described in U.S. Pat. No. 4,373,666, for example, the bypass valve is connected to the tubes or hoses for liquid flow through the heater by means of devices such as clamping collars, or the like. This means that assembly on the manufacturing line for the vehicle as a whole takes a relatively long time, and in addition there is a danger of leakage from the mechanical device constituting the bypass valve per se, or even of damage thereto. In addition, account must be taken of the desire of vehicle manufacturers to reduce assembly time, and numbers of assembly and inspection personnel, while simultaneously reducing as much as possible any risk of damaging components or of leaks appearing after assembly, thereby giving rise to a problem in the vehicle manufacturing industry of providing a bypass valve device which avoids the above-mentioned drawbacks of prior art devices.